The measurement of the pH level within the interior of the stomach has long been recognized as a method of diagnosis of a patient's condition. An early method for measuring the pH level included the insertion of a hollow tube into the patient's nose and through the esophagus to the stomach. Stomach fluids were then removed through the tube by aspiration and collected. Once collected, the fluids were tested for acidity.
In an attempt to measure the pH level of the stomach without using such a tube, an in vivo device which could be swallowed and subsequently removed for pH analysis was devised. Such a device is described in U.S. Pat. No. 3,528,429 issued to Beal et al. Described therein is a capsule containing coiled string which is coated with a pH indicator. One end of the string is held while the capsule is swallowed. The string is then removed, permitting a visual inspection of the pH indicator. While such a device was adequate for situations where the patient was in a non-critical condition and could cooperate in the process, it was not adequate for situations where the patient was suffering from shock, a condition which can be monitored by measuring intramuscosal pH in the stomach.
As discussed in an article by R. G. Riddian-Green et al. in Goals for the Resuscitation of Shock, Critical Care Medicine 1993, 21:525-531, the measurement of tissue pH provides an indication of the tissue oxygenation abilities of the patient. These abilities are especially important in determining whether a patient has been fully resuscitated from shock. Conventional methods for determining resuscitation from Shock, such as monitoring blood pressure, heart rate, cardiac output, hematocrit determinations, and blood gases, are not adequate for determining complete and optimal resuscitation.
Thus, Riddian-Green et al. proposed using an intraluminally located gastrointestinal tonometer for indirect measurement of intramuscosal pH in the stomach. The tonometer included a saline filled balloon which was placed in the stomach. CO.sub.2 in the balloon saline then equilibrated with the mucosal CO.sub.2. In this way, the tonometer provided a measurement of PCO.sub.2 which was used with a simultaneous measurement of arterial carbonate in determining mucosal pH as calculated by the Henderson-Hasselbalch equation. Once the mucosal pH was calculated, a more complete picture of the patient's resuscitation from shock, was possible as the tissue oxygenation abilities were known.
Using a gastrointestinal tonometer of the type described in the Riddian-Green et al. article requires a nasogastric tube dedicated for such use. Where other operations, such as aspiration of the stomach, are to be performed in conjunction with the measurement of stomach pH, two or more nasogastric tubes are required. As the cross-sectional area of the nasogastric tract is limited, the use of two or more tubes is an inefficient method of utilizing the available area of the tract.
Thus, it would be highly desirable to have an apparatus, and a method of using it, for performing multiple tasks relating to the gastrointestinal system, including the determination of the stomach pH. The apparatus, and method of using it, should utilize the available cross-sectional area in an efficient manner.
Such an apparatus, and the associated method, should include a nasogastric tube for providing unobstructed access to the stomach from outside of the patient's body which can perform many functions, thereby reducing patient discomfort by repeated insertion and removal of the tube. Multipassagewayed tubes have been proposed in the past which could perform more than one function. These include the tubes described in U.S. Pat. Nos. 3,593,713; 4,280,501, 4,584,998, 4,735,607, 5,076,268 and 5,176,638.
All of the tube patents named above describe a somewhat rigid tube which does not conform easily to the nasogastric passage during insertion, causing great discomfort to the patient, and which are prone to being pinched down, blocking access to the stomach, at the 90 degree bend as the tube passes from the nasal cavity to the esophagus at the back of the throat.
U.S. Pat. No. 5,085,216 describes a tube which is completely collapsible for comfort. A stiffener, having a pH indicator attached thereto, is inserted into the tube for insertion. The pH indicator shows whether the tube has been correctly inserted. Once inserted, the stiffener and pH indicators are removed and the patient can then be fed. Although many functions can be performed by the tube, they cannot be done simultaneously.
Thus, it would also be desirable to have an apparatus, and method of using it, for continuously monitoring stomach pH which uses a partially collapsible nasogastric tube having multiple passageways and which can be inserted into the nasogastric tract without causing large amount of patient discomfort and which will not be closed off, blocking the passage between both ends of the tube.
Once the nasogastric tube is in place, it often happens that the patient is required to change positions. As a result of the position change, the tube is moved within the nasogastric passage, chaffing sensitive tissue within the nasal cavity. To prevent tube movement after the tube is inserted in previous tube arrangements, an inflatable balloon has been provided at the distal end of the tube to hold the end firmly in place. After the tube is inserted and the distal end is at the desired location, the balloon is inflated to expand outwardly, thereby pressing against the inner wall of the nasogastric tract. However, such an arrangement still permits the tube to move and rub against delicate nasal cavity tissue.
Thus, it would further be desirable to have such an apparatus, and a method of using it, which could be held in place to prevent movement of the tube within the nasal cavity.